(Not Applicable)
(Not Applicable)
The present invention generally relates to identification systems and more particularly to an optical identification system that has a low probability of being intercepted.
Military operations frequently require location and identification of friendly personnel or vehicles over line-of-sight ranges of a few miles. Typically, a field commander will want to visually identify units to determine their position in the field. By knowing the exact position of the units in the field, the field commander can move his personnel and vehicles into an optimum position.
Determining the position of personnel and vehicles in the field can be difficult due to battlefield conditions. Personnel and vehicles may be camouflaged such that a visual identification may be difficult. Additionally, personnel and vehicles may be turned away from the battlefield commander such that markings on the vehicle cannot be seen and a positive identification cannot be made.
In prior art identification systems, the battlefield commander has used a radio to interrogate field units and determine their positions. However, this method could lead to detection by enemy units through radio direction finding techniques. Alternatively, even if the enemy cannot determine the exact location of the battlefield units, the enemy will still be informed of the units presence through their radio communications. Therefore, radio identification of battlefield units is not desirable because it is susceptible to interception by the enemy.
Prior art optical identification systems have relied upon a laser beam for interrogation of units. In such systems, the battlefield commander will direct a laser beam from a transmitter onto a target located on the desired unit. The target will respond by transmitting its own laser back to a receiver whereby information contained within the laser beam about the identification of the unit will be decoded. Alternatively, the target may modify the transmitted beam and return the modified beam to the battlefield commander whereby the modified beam will be decoded in order to determine the identification of the unit. A problem associated with the prior art laser identification systems is that the systems are bulky and highly complex. In this respect, the transmitter and target are highly complex and prone to failure. Additionally, the lasers used in the prior art systems are bulky and consume large amounts of power thereby needing to be cooled and making it difficult to implement a portable system for the battlefield. Further, a problem associated with the prior art optical identification systems is that the laser beam is subject to divergence and scattering thereby allowing such systems to be vulnerable to detection and jamming by the enemy.
The present invention addresses the problems associated with the prior art identification systems by providing a system that provides covert identification of units on the battlefield. In this respect, the present invention provides an optical identification system that is easily transportable and consumes a low amount of power. Further, the present invention provides a laser based optical identification system that is extremely difficult to detect and jam.
An optical identification system for identifying a vehicle. The system comprises a laser source for generating a transmitted beam and a reflector in optical communication therewith. The reflector is operative to reflect the transmitted beam to thereby generate a reflected beam. The system further includes a shutter in optical communication with the reflected beam and operative to modulate the polarization of the reflected beam with identification information to thereby generate a modulated reflected beam. The optical identification system further includes a detector in optical communication with the reflected beam. The detector is operative to pass the modulated reflected beam and decode the identification information modulated thereon.
In the preferred embodiment of the present invention, the detector of the optical identification system will include a polarizer to pass the correct polarization of the reflected beam. The polarizer is configured to pass the modulated reflected beam when the polarization of the modulated reflected beam matches the polarization modulated by the shutter. The detector of the optical identification system further includes an optical filter that is operative to only pass the modulated reflected beam when the wavelength thereof matches the wavelength of the transmitted beam.
Typically, the laser source and the detector will be mounted on a common platform such as a pair of binoculars to form a sighting device. The laser is a low power (20 mW) eye safe laser that emits light having a wavelength of about 1.55 xcexcm.
The shutter and the reflector of the present invention will be mounted as a target upon the vehicle to be identified. In this respect, the shutter will be an electronically driven liquid crystal that modulates the reflected beam by rotating the polarization thereof. Typically, the shutter will modulate the polarization with a prescribed code that is the identification information. In the preferred embodiment of the present invention, the identification information corresponds to the identity of the vehicle. The reflector is typically a corner cube operative to reflect the transmitted beam back to the source. The shutter will be mounted in front of the corner cube such that the transmitted beam must pass through the shutter before striking the reflector.
The detector of the present invention is a photodetector operative to convert the modulated reflected beam into an electrical signal. The detector is configured to decode the modulated reflected beam to determine the identification information.
In accordance with the present invention, there is Provided a method of optical identification with a laser source, a shutter, a reflector, a polarizer and a detector. The method comprises generating a transmitted beam with the laser source. Next, the transmitted beam is reflected with the reflector to generate a reflected beam. The polarization of the reflected beam is modulated with identification information by the shutter to thereby generate a modulated reflected beam. The modulated reflected beam is passed by the polarizer when the polarization of the modulated reflected beam matches the polarization modulated by the shutter. The modulated reflected beam is decoded with the detector to determine the identification information. Typically, the reflector and the shutter are mounted on a vehicle and the identification information modulated on the reflected beam corresponds to an identification code of the vehicle.